Abstract
A 70-year-old woman with anti-aminoacyl-tRNA synthetase (ARS) antibody-positive interstitial lung disease (ARS-ILD) received daily medications and regular cyclophosphamide cycles for recurring exacerbations. Approximately four years after immunosuppression initiation, the patient was admitted for progressive dyspnea on exertion. Chest computed tomography (CT) findings were suggestive of acute exacerbation. Despite intensified immunosuppressive treatment, the radiographic findings worsened, and serum Krebs von den Lungen-6 (KL-6) levels increased. A bronchoalveolar lavage fluid (BALF) examination revealed amorphous globules and alveolar macrophages with eosinophilic granules. Owing to negative anti-granulocyte-macrophage colony-stimulating factor antibody tests, a diagnosis of secondary pulmonary alveolar proteinosis (PAP) was established.